The present disclosure relates to a semiconductor memory device, and more particularly, to the wiring structure of a nonvolatile memory device.
A semiconductor memory device may be a volatile semiconductor memory device or a nonvolatile semiconductor memory device.
Although the read and write speeds of a volatile semiconductor memory device are fast, data that are stored in the volatile semiconductor memory device are erased when an external power supply source is shut off. On the other hand, even when an external power supply source is shut off, the nonvolatile semiconductor memory device retains stored data. Therefore, the nonvolatile semiconductor memory device is used to store data to be retained irrespective of whether the external power supply source is on or off. Examples of nonvolatile semiconductor memory devices include Mask Read-Only Memory (MROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM) and Electrically Erasable Programmable Read-Only Memory (EEPROM).
In MROM, PROM and EPROM, generally, it is difficult to update stored data because it is inconvenient to autonomously erase and write data. In comparison, EEPROM may electrically erase and write data, so uses of EEPROM for system programming and auxiliary memory devices which require continuous updates are being expanded. Also, flash EEPROM in particular has a higher degree of integration than the existing EEPROM, and is therefore easily incorporated as large-capacity auxiliary memory devices. Flash EEPROM includes NAND-type flash EEPROM (hereinafter referred to as a NAND-type flash memory), for example, which has a higher degree of integration than other types of flash EEPROM.